1. Field of the Invention
The present invention relates generally to compositions and methods for preventing, treating and detecting leishmaniasis in patients. More particularly, the invention relates to compositions comprising Leishmania sterol 24-c-methyltransferase (SMT) polypeptides, fusion polypeptides thereof, as well as polynucleotides encoding such polypeptides and fusions.
2. Background of the Related Art
Human leishmaniasis is a spectrum of diseases caused by protozoan parasites of the genus Leishmania. Leishmaniases are roughly classified into three types of diseases, cutaneous leishmaniasis (CL), mucosal leishmaniasis (ML) and visceral leishmaniasis (VL), according to the clinical manifestations. Visceral leishmaniasis, generally caused by species of the L. donovani complex, i.e., L. donovani and L. infantum (chagasi), is the most severe form, with approximately 500,000 new cases reported annually (information from World Health Organization: www dot who dot int/leishmaniasis/en/). Active VL is characterized by hematological and hepatosplenic abnormalities, and is generally fatal unless properly treated.
Leishmania parasites are transmitted by the bite of sandflies and the infecting promastigotes differentiate into and replicate as amastigotes within macrophages in the mammalian host. In common with other intracellular pathogens, cellular immune responses are critical for protection against leishmaniasis. Th1 immune responses play an important role in mediating protection against Leishmania, including roles for CD4+ and CD8+ T cells, IFN-γ, IL-12, TNF-α and NO, whereas inhibitory effects have been reported for IL-10 and TGF-β (Engwerda et al., (1998) Eur J Immunol 28:669-680; Murphy et al., (2001) Eur J Immunol 31:2848-2856; Murray and Nathan. (1999) J Exp Med 189:741-746; Murray et al., (2000) Infect Immun 68:6289-6293; Squires et al., (1989) J Immunol 143:4244-4249; Taylor and Murray. (1997) J Exp Med 185:1231-1239; Kaye and Bancroft. (1992) Infect Immun 60:4335-4342; Stern et al., (1988) J Immunol 140:3971-3977; and Wilson et al., (1998) J Immunol 161:6148-6155). Immunization against leishmaniasis in animal models can be effected by delivery of antigen-encoding DNA vectors (Gurunathan et al., (1997) J Exp Med 186:1137-1147; Piedrafita et al., (1999) J Immunol 163:1467-1472; and Mendez et al., (2001) J Immunol 166:5122-5128) or by administration of proteins formulated with Th1-inducing adjuvants including IL-12 (Afonso et al., (1994) Science 263:235-237; Stobie et al., (2000) Proc Natl Acad Sci USA 97:8427-8432; and Kenney et al., (1999) J Immunol 163:4481-4488) or TLR ligands such as CpG oligonucleotides (Rhee et al., (2002) J Exp Med 195:1565-1573; Stacey and Blackwell. (1999) Infect Immun 67:3719-3726; and Walker et al., (1999) Proc Natl Acad Sci USA 96:6970-6975) and monophosphoryl lipid A (Coler et al., (2002) Infect Immun 70:4215-4225 and Skeiky et al., (2002) Vaccine 20:3292-3303).
In spite of evidence that sub-unit vaccines may be effective in models of VL (Basu et al., (2005) J Immunol 174:7160-7171; Stager et al., (2000) J Immunol 165:7064-7071; Ghosh et al., (2001) Vaccine 20:59-66; Wilson et al., (1995) Infect Immun 63:2062-2069; Tewary et al., (2005) J Infect Dis 191:2130-2137; Aguilar-Be et al., (2005) Infect Immun 73:812-819; and Rafati et al., (2006) Vaccine 24:2169-2175), progress toward defining bona fide antigen candidates effective against VL in vivo has been lacking Several L. infantum antigens have been identified by serological screening using sera from L. infantum-infected hamsters (Goto et al., (2006) Infect Immun 74:3939-3944). Sterol 24-c-methyltransferase (SMT), one of the antigens found to be reactive, is an enzyme involved in biosynthesis of ergosterol, which is a target molecule of leishmanicidal and fungicidal amphotericin B (Pourshafie et al., (2004) Antimicrob Agents Chemother 48:2409-2414). Amphotericin B shows selective killing activity selectively against some protozoan parasites and fungi, as ergosterol is not found in mammalian cells. Similarly, SMT is found in several parasites, fungi and plants, but is absent in mammals.
Strategies employing vaccines consisting of whole organisms for preventing or treating leishmaniasis have not been effective in humans. Accordingly, there remains a significant need for immunogenic compositions and vaccines that can effectively prevent and/or treat leishmaniasis in humans and other mammals (e.g., canines). The present invention fulfills these needs and offers other related advantages